The present invention relates to improvements in motion transmitting assemblies, and more particularly to improvements in assemblies wherein a rotary driving member transmits torque to a rotary driven member. Still more particularly, the invention relates to improvements in assemblies wherein the driving and driven members must or should be hermetically sealed from each other. Typical examples of assemblies which can embody the present invention are shaft seals.
Shaft seals are necessary in certain types of pumps, valves, measuring apparatus, regulating apparatus and in many other systems wherein aggressive media must be confined and/or compelled to remain in a predetermined path or wherein the conveyed media must be shielded from the surrounding atmosphere. For example, it is often necessary to hermetically seal certain gaseous and/or liquid media from the surrounding area. Hermetic seals are invariably necessary when the driving and driven members are mounted in areas (e.g., in separate chambers or compartments) which must be maintained at different pressures, e.g., if the driving member is disposed in an area wherein the pressure matches or approximates atmospheric pressure but the driven member is to be confined in an evacuated chamber or compartment wherein the pressure is or should be well below atmospheric pressure.
German Offenlegungsschrift No. 15 50 699 discloses a vacuum-tight shaft seal wherein one end portion of the driven shaft is bent and is rotatably mounted in a thimble-like motion transmitting member which, in turn, is sealingly secured to a bellows and has a pin serving to transmit motion to a crank disc. The crank disc can cause the driven shaft to rotate by compelling the bent end portion of such shaft to orbit about the axis of the driven shaft. A drawback of the just described shaft seal is that it occupies a substantial amount of space as well as that the transmission of torque cannot take place without play which eliminates such seals from utilization under circumstances when the transmission of motion should be effected with a high or utmost degree of accuracy.
German Auslegeschrift No. 11 31 054 discloses an assembly which can transmit only oscillatory movements and wherein the adjoining end portions of two shafts have crank pins which are disposed opposite each other. A crank web between the two shafts has two blind bores each of which receives one of the pins. One end portion of a sealing device in the form of a bellows is sealingly secured to a housing and its other end portion is affixed to the web. During transmission of oscillatory motion, the web oscillates about the common axis of the two shafts. Studs which extend into complementary grooves of finite length confine the crank web to oscillatory movements of predetermined maximum amplitude. The Auslegeschrift mentions the possibility of replacing the grooves of finite length with endless annular grooves so as to allow for rotary movements of the shafts. However, the publication does not explain how such rotary movements can take place due to the fact that the movements of the shafts to certain angular positions (namely to the right-hand and left-hand dead end positions) apparently entail a tilting and resulting blocking, even if one disregards the unavoidable machining tolerances. Therefore, the Auslegeschrift further proposes to use a planetary transmission if the driven shaft is to receive an uninterrupted rotary motion. Such transmission enables the driver shaft to continuously transmit torque in a controlled manner.
A similar assembly is disclosed in German Pat. No. 12 33 668 wherein two slides are installed in straight grooves. In other respects, the patented assembly is identical with or clearly analogous to the assembly of the aforementioned Auslegeschrift.